Various types of hearing prostheses may provide persons with different types of hearing loss with the ability to perceive sound. Hearing loss may be conductive, sensorineural, or some combination of both conductive and sensorineural hearing loss. Conductive hearing loss typically results from a dysfunction in any of the mechanisms that ordinarily conduct sound waves through the outer ear, the eardrum, or the bones of the middle ear. Sensorineural hearing loss typically results from a dysfunction in the inner ear, including the cochlea, where sound vibrations are converted into neural signals, or any other part of the ear, auditory nerve, or brain that may process the neural signals.
Persons with some forms of conductive hearing loss may benefit from hearing prostheses, such as acoustic hearing aids or vibration-based hearing aids. An acoustic hearing aid typically includes a small microphone to detect sound, an amplifier to amplify certain portions of the detected sound, and a small speaker to transmit the amplified sounds into the person's ear. Vibration-based hearing aids typically include a small microphone to detect sound, and a vibration mechanism to apply vibrations corresponding to the detected sound to a person's bone, thereby causing vibrations in the person's inner ear, thus bypassing the person's auditory canal and middle ear. Vibration-based hearing aids may include bone anchored hearing aids, direct acoustic cochlear stimulation devices, or other vibration-based devices.
A bone anchored hearing aid typically utilizes a surgically-implanted mechanism to transmit sound via direct vibrations of an implant recipient's skull. An external component of the vibration-based hearing aid detects sound waves, which are converted into a series of electrical stimulation signals delivered to the implant recipient's skull bones via an electromechanical transducer (e.g., a mechanical actuator). By providing a stimulation to the recipient's skull, the bone anchored hearing aid enables the recipient's middle ear and auditory canal to be bypassed, which is advantageous for recipients with medical conditions that affect the middle or outer ear. The vibrations of the recipient's skull bones cause fluid motion within the recipient's cochlea, thereby enabling the recipient to perceive sound based on the vibrations. Similarly, a direct acoustic cochlear stimulation device typically utilizes a surgically-implanted mechanism to transmit sound via direct vibrations of the cochlea. Other non-surgical vibration-based hearing aids may use similar vibration mechanisms to transmit sound via direct vibration of a recipient's teeth or other cranial or facial bones.